Broad objectives. This study aims to describe and explain the relationship between age and changes in the sense of control over one's life. Specific aims. Four preliminary cross-sectional surveys show that the average sense of control declines in successively older age groups beginning in late middle age. The current study measures change in the sense of control over a three-year follow-up period, correlates the changes with age, and tests hypotheses about the form and components of the association. The main hypotheses are: (I) Dover a period of time, the sense of control declines by an amount that increases with age; (II) the change in sense of control reflects an underlying change in biosocial function, which accelerates with age; (III) higher social status slows the decline in the sense of control, possibly by preserving biosocial function; and (IV) changes in biosocial function and in the sense of control have deviation-amplifying reciprocal effects that accelerate age-dependent changes in the sense of control. Health relatedness. If Rodin's theory of aging dynamics is correct, a sense of control over one's life increases active participation and improves emotional well-being and physical function, which in turn bolsters the sense of control. Emotional well-being and physical function are health factors themselves, and they decrease subsequent morbidity and mortality. Study design and methods. The study surveys a national sample of persons ages l8 and over. Respondents were selected at random and first interviewed by telephone in late 1994 or early 1995. Persons age 60 and older were over-sampled by 80 percent. The design calls for three waves of interviews three years apart. Collection of the second wave will be complete in Spring of 1998. The application requests continued support for analysis of data from the first two waves, and support for collecting and analyzing a third wave of data. The analyses will specify models that test the hypotheses and address technical issues such as measurement error and non-random attrition.